如何在SQL SELECT语句中执行IF…THEN?
例如:
SELECT IF(Obsolete = 'N' OR InStock = 'Y' ? 1 : 0) AS Saleable, * FROM Product
如何在SQL SELECT语句中执行IF…THEN?
例如:
SELECT IF(Obsolete = 'N' OR InStock = 'Y' ? 1 : 0) AS Saleable, * FROM Product
当前回答
我喜欢使用CASE语句,但问题是在SQLSelect中使用IF语句。我过去使用的是:
SELECT
if(GENDER = "M","Male","Female") as Gender
FROM ...
这就像Excel或sheets IF语句,其中有一个条件,后跟true条件,然后是false条件:
if(condition, true, false)
此外,您还可以嵌套if语句(但use应该使用CASE:-)
(注意:这在MySQL Workbench中有效,但在其他平台上可能不起作用)
其他回答
CASE语句最接近SQL中的IF,并且在所有版本的SQL Server上都受支持。
SELECT CAST(
CASE
WHEN Obsolete = 'N' or InStock = 'Y'
THEN 1
ELSE 0
END AS bit) as Saleable, *
FROM Product
如果希望结果为布尔值,则只需使用CAST运算符。如果您对int感到满意,这将起作用:
SELECT CASE
WHEN Obsolete = 'N' or InStock = 'Y'
THEN 1
ELSE 0
END as Saleable, *
FROM Product
CASE语句可以嵌入到其他CASE语句中,甚至可以包含在聚合中。
SQL Server Denali(SQL Server 2012)添加了IIF语句,该语句也可用于访问(Martin Smith指出):
SELECT IIF(Obsolete = 'N' or InStock = 'Y', 1, 0) as Saleable, * FROM Product
问题:
SELECT IF(Obsolete = 'N' OR InStock = 'Y' ? 1 : 0) AS Saleable, * FROM Product
答案:
Select
case when p.Obsolete = 'N'
or p.InStock = 'Y' then 1 else 0 end as Saleable,
p.*
FROM
Product p;
使用别名(在本例中为p)将有助于防止出现问题。
SELECT 1 AS Saleable, *
FROM @Product
WHERE ( Obsolete = 'N' OR InStock = 'Y' )
UNION
SELECT 0 AS Saleable, *
FROM @Product
WHERE NOT ( Obsolete = 'N' OR InStock = 'Y' )
SELECT
(CASE
WHEN (Obsolete = 'N' OR InStock = 'Y') THEN 'YES'
ELSE 'NO'
END) as Salable
, *
FROM Product
case statement some what similar to if in SQL server
SELECT CASE
WHEN Obsolete = 'N' or InStock = 'Y'
THEN 1
ELSE 0
END as Saleable, *
FROM Product